The Pechmann condensation is a reaction in which phenols and β-keto esters react under acid catalysis to synthesize coumarin derivatives. It was first discovered by German chemist Hans Freiherr von Pechmann and is named after him. Coumarins are important intermediates in pharmaceuticals, agrochemicals, and functional materials. This reaction offers a valuable synthetic tool for the preparation of coumarins and is considered an effective method for producing them from activated phenols.

Under acidic conditions, phenols and β-keto esters first undergo esterification, followed by Michael addition, rearomatization, and finally acid-induced dehydration to afford the coumarin products.

• Reagents: Brønsted acids or Lewis acids

• Reactants: β-keto esters, phenols

• Products: Coumarin derivatives

• Reaction Type: Condensation

Experimental Tips:

• Electron-donating groups on phenols facilitate the reaction, while electron-withdrawing groups hinder it.

• The choice of acid significantly affects the reaction; if the desired result is not obtained, it may help to try a different acid.

• For simple phenols, harsher conditions are typically required (e.g., heating and strong acids), but for highly activated phenols such as resorcinol, the reaction can proceed at room temperature.

Reaction Mechanism

Original Literature

H. von Pechmann, C. Duisberg. Berichte der deutschen chemischen Gesellschaft, 1883, 16(2), 2119–2128.

Key References:

• An efficient procedure for the synthesis of coumarin derivatives using TiCl₄ as catalyst under solvent-free conditions. Tetrahedron Letters, 2005, 46(20), 3501–3503.

• Synthesis of 7-substituted 4-methyl coumarins by Pechmann reaction using nano-crystalline sulfated-zirconia. Journal of Molecular Catalysis A: Chemical, 2007, 276(1–2), 47–56.